U.S. patent application number 11/566814 was filed with the patent office on 2008-06-05 for method for doping impurities.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Greg Thomas Dunne, Stanislav Ivanovich Soloviev, Zachary Matthew Stum, Jesse Berkley Tucker.
Application Number | 20080132047 11/566814 |
Document ID | / |
Family ID | 39476340 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080132047 |
Kind Code |
A1 |
Dunne; Greg Thomas ; et
al. |
June 5, 2008 |
METHOD FOR DOPING IMPURITIES
Abstract
A method for doping impurities into a device layer is provided.
The method includes providing a carbonized dopant layer over a
device layer, wherein the carbonized dopant layer comprises one or
more dopant impurities, and heat treating the carbonized dopant
layer to thermally diffuse the dopant impurities into the device
layer.
Inventors: |
Dunne; Greg Thomas;
(Rexford, NY) ; Tucker; Jesse Berkley;
(Schenectady, NY) ; Soloviev; Stanislav Ivanovich;
(Albany, NY) ; Stum; Zachary Matthew; (Niskayuna,
NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
39476340 |
Appl. No.: |
11/566814 |
Filed: |
December 5, 2006 |
Current U.S.
Class: |
438/527 ;
257/E21.473 |
Current CPC
Class: |
H01L 21/2258 20130101;
H01L 21/0455 20130101 |
Class at
Publication: |
438/527 ;
257/E21.473 |
International
Class: |
H01L 21/425 20060101
H01L021/425 |
Claims
1. A method for doping impurities into a device layer comprising:
providing a carbonized dopant layer over a device layer, wherein
the carbonized dopant layer comprises one or more dopant
impurities; and heat treating the carbonized dopant layer to
thermally diffuse the dopant impurities into the device layer.
2. The method of claim 1, wherein providing the carbonized dopant
layer comprises: disposing a carbon-based dopant material, wherein
the carbon-based dopant material comprises the one or more dopant
impurities; and carbonizing the carbon-based dopant material to
form a carbonized dopant layer.
3. The method of claim 2, wherein disposing the carbon-based dopant
material comprises spin coating the carbon-based dopant material
over the device layer.
4. The method of claim 2, wherein carbonizing the carbon-based
dopant material to form the carbonized dopant layer comprises
heating the carbon-based dopant material to a temperature in a
range from about 500.degree. C. to about 1500.degree. C.
5. The method of claim 2, wherein the carbon-based dopant material
comprises a carbon material.
6. The method of claim 2, wherein the carbon-based material
comprises a photoresist material.
7. The method of claim 1, wherein providing a carbonized dopant
layer over a device layer comprises vapor depositing or
co-sputtering to deposit the carbonized dopant layer, wherein the
carbonized dopant layer comprises carbon and one or more dopant
impurities.
8. The method of claim 1, wherein heat treating the carbonized
dopant layer comprises annealing the carbonized dopant layer.
9. The method of claim 8 wherein annealing comprises annealing at a
temperature in a range from about 1000.degree. C. to about
2500.degree. C.
10. The method of claim 1, wherein the one or more impurities
comprise n-type dopants, p-type dopants, optical dopants or
magnetic dopants.
11. The method of claim 1, wherein the one or more impurities
comprise dopants comprising aluminum, boron, gallium, magnesium
phosphorus, arsenic, calcium, beryllium, iron, antimony, nitrogen,
silicon, or any combination thereof.
12. The method of claim 1, wherein the one or more impurities
comprise magnetic dopants comprising manganese, cobalt, iron or any
combination thereof.
13. The method of claim 1, wherein the one or more impurities
comprise optical dopants comprising zinc, rare earth elements or
any combination thereof.
14. The method of claim 1, wherein the device layer comprises a
material comprising Si, AlN, InN, or AlGaN.
15. The method of claim 1, wherein the device layer comprises
SiC.
16. The method of claim 1, wherein the device layer comprises
GaN.
17. The method of claim 1, further comprising providing a
carbonized photoresist layer over the carbonized dopant layer prior
to heat treating the carbonized dopant layer to protect the
carbonized dopant layer during heat treating.
18. The method of claim 1, wherein the carbonized dopant layer
comprises a patterned carbonized dopant layer.
19. The method of claim 1, further comprising removing the
carbonized dopant layer after heat treatment.
20. The method of claim 19, wherein removing the carbonized dopant
layer comprises burning the carbonized dopant layer in an oxygen
environment.
21. The method of claim 1, wherein providing a carbonized dopant
layer comprises: coating a surface of the device layer with a
carbon-based material; carbonizing the carbon-based material to
form a carbonized layer; and implanting dopant impurities into the
carbonized layer to form the carbonized dopant layer.
22. The method of claim 1, wherein providing a carbonized dopant
layer comprises: coating a substrate with a carbon-based dopant
material, wherein the carbon-based dopant material includes one or
more impurities; carbonizing the carbon-based dopant material to
form a carbonized dopant layer; removing the carbonized dopant
layer from the substrate; and disposing the carbonized dopant layer
over the device layer.
23. The method of claim 22, further comprising patterning the
carbonized dopant layer prior to removing the carbonized dopant
layer from the substrate.
24. The method of claim 1, further comprising patterning the
carbonized dopant layer by reactive ion etching prior to heat
treating the carbonized dopant layer.
25. The method of claim 1, further comprising disposing a nitride
layer to protect the carbonized dopant layer during patterning and
etching processes.
26. A method for doping impurities into a device layer comprising:
disposing a carbon-based dopant material, wherein the carbon-based
dopant material comprises one or more dopant impurities;
carbonizing the carbon-based material to form a carbonized dopant
layer; and heat treating the carbonized dopant layer to thermally
diffuse the dopant impurities into the device layer.
27. The method of claim 26, further comprising patterning the
carbon-based dopant material prior to carbonizing the carbon-based
dopant material.
28. The method of claim 26, wherein patterning the carbon-based
dopant material comprises performing photolithography of the
carbon-based dopant material.
29. The method of claim 26, further comprising disposing a
photoresist layer over the device layer and patterning the
photoresist layer prior to disposing the carbon-based dopant
material.
30. The method of claim 26, further comprising disposing a
photoresist layer over the carbon-based dopant material subsequent
to patterning the carbon-based dopant material and prior to
carbonizing the carbon-based dopant material.
31. A method for fabricating a semiconductor device, the method
comprising: providing a first carbonized dopant layer over a device
layer, wherein the carbonized dopant layer comprises one or more
first dopant impurities; heat treating the first carbonized dopant
layer to thermally diffuse the first dopant impurities into the
device layer; removing the first carbonized dopant layer; providing
a second carbonized dopant layer over the device layer subsequent
to removal of the first carbonized dopant layer, wherein the second
carbonized dopant layer comprises one or more second dopant
impurities; and heat treating the second carbonized dopant layer to
thermally diffuse the second dopant impurities into the device
layer.
32. The method of claim 31, wherein heat treating the second
carbonized dopant layer results in the first dopant impurities
being driven deeper into the device layer to create a gradient in
the dopant impurity distribution in the device layer.
33. The method of claim 31, wherein the first and second dopant
impurities are of different dopant types.
34. The method of claim 31, wherein the semiconductor device is a
transistor.
35. The method of claim 31, wherein the semiconductor device is a
diode device.
36. A method for fabricating a semiconductor device, the method
comprising: providing a first patterned carbonized dopant layer
over a device layer, wherein the carbonized dopant layer comprises
one or more first type dopant impurities; providing a second
carbonized dopant layer over the first patterned carbonized dopant
layer and partly in contact with the device layer, wherein the
second carbonized dopant layer comprises one or more second type
dopant impurities different from the first type dopant impurities;
and heat treating the first patterned carbonized dopant layer and
second carbonized dopant layer to thermally diffuse the first and
second dopant impurities in a patterned device structure.
37. The method of claim 36, wherein the semiconductor device is a
transistor.
38. The method of claim 36, wherein the semiconductor device is a
diode device.
Description
BACKGROUND
[0001] The invention relates generally to a method for doping
impurities into semiconductor device layers and more particularly,
the invention relates to a solid phase diffusion method for doping
impurities into semiconductor device layers.
[0002] Currently, doped areas in wafers are created in one of a few
ways. In one method, a semiconductor layer is grown with the dopant
impurity in the gas stream during epitaxial growth of the
semiconductor layer. The wafer can then be patterned and etched
leaving doped regions. Epitaxy is typically conformal and
non-selective.
[0003] In another method, a pattern is made on a wafer or on top of
an epitaxially grown layer. Impurities are then ion implanted by
controlling the dose and power. Although ion implantation can be
selectively performed, it often leaves a damaged matrix and
requires a subsequent annealing process to embed the dopant
impurity within the matrix.
[0004] A method for doping impurities without the drawbacks of the
current techniques would therefore be desirable.
BRIEF DESCRIPTION
[0005] One embodiment of the present invention is a method for
doping impurities into a device layer. The method includes
providing a carbonized dopant layer over a device layer, wherein
the carbonized dopant layer comprises one or more dopant
impurities, and heat treating the carbonized dopant layer to
thermally diffuse the dopant impurities into the device layer.
[0006] Another embodiment of the present invention is a method for
doping impurities into a device layer with the method including
disposing a carbon-based dopant material, wherein the carbon-based
dopant material comprises one or more dopant impurities,
carbonizing the carbon-based material to form a carbonized dopant
layer, and heat treating the carbonized dopant layer to thermally
diffuse the dopant impurities into the device layer.
[0007] Still another embodiment of the present invention is a
method for fabricating a semiconductor device. The method includes
providing a first carbonized dopant layer over a device layer,
wherein the carbonized dopant layer includes one or more first
dopant impurities, heat treating the first carbonized dopant layer
to thermally diffuse the first dopant impurities into the device
layer, removing the first carbonized dopant layer, providing a
second carbonized dopant layer over the device layer subsequent to
removal of the first carbonized dopant layer, wherein the second
carbonized dopant layer comprises one or more second dopant
impurities, and heat treating the second carbonized dopant layer to
thermally diffuse the second dopant impurities into the device
layer.
[0008] Yet another embodiment of the present invention is a method
for fabricating a semiconductor device wherein the method includes
providing a first patterned carbonized dopant layer over a device
layer, wherein the carbonized dopant layer comprises one or more
first type dopant impurities, providing a second carbonized dopant
layer over the first patterned carbonized dopant layer and partly
in contact with the device layer, wherein the second carbonized
dopant layer comprises one or more second type dopant impurities
different from the first type dopant impurities, and heat treating
the first patterned carbonized dopant layer and second layer to
thermally diffuse the first and second dopant impurities in a
patterned device structure.
DRAWINGS
[0009] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0010] FIG. 1 is a flow chart illustrating a method for diffusing
impurities into a device layer in accordance with one embodiment of
the present invention.
[0011] FIG. 2 is a flow chart illustrating a method for diffusing
impurities into a device layer in accordance with one embodiment of
the present invention.
[0012] FIG. 3 is a schematic representation of a method for doping
impurities into a device layer in accordance with one embodiment of
the present invention.
[0013] FIG. 4 is a flow chart illustrating a method for diffusing
impurities into a device layer in accordance with one embodiment of
the present invention.
[0014] FIG. 5 is a schematic representation of a method for doping
impurities into a device layer in accordance with one embodiment of
the present invention.
[0015] FIG. 6 is a schematic representation of a method for
fabricating a device in accordance with one embodiment of the
present invention.
[0016] FIG. 7 is a schematic representation of a method for
fabricating a device in accordance with one embodiment of the
present invention.
[0017] FIG. 8 is a schematic representation of a method for
fabricating a device in accordance with one embodiment of the
present invention.
DETAILED DESCRIPTION
[0018] Embodiments of the present invention include methods for
doping impurities into device layers, particularly semiconductor
device layers. As used herein, the term "device layer" refers to
any layer in a device, for example, an active device layer or a
substrate layer in a semiconductor device. The device layer may be
semiconducting prior to the diffusion of impurities in accordance
with one embodiment of the present invention. The layer may also be
rendered semiconducting upon diffusion of impurities in accordance
with another embodiment of the present invention.
[0019] One embodiment of the present invention is a method for
doping impurities into a device layer using a carbonized dopant
film including one or more impurities disposed over the device
layer. A thermal diffusion process is used to diffuse the
impurities into the device layer either conformally or
selectively.
[0020] FIG. 1 is a flow chart illustrating a method 10 for doping
impurities into a device layer in accordance with one embodiment of
the present invention. In step 12, a carbonized dopant layer is
provided over a device layer. The carbonized dopant layer includes
one or more dopant impurities.
[0021] Non-limiting examples of dopant impurities include aluminum,
boron, gallium, phosphorus, arsenic, antimony, and nitrogen. In one
embodiment, the dopant impurities are acceptor type impurities such
as boron. In another embodiment, the dopant impurities are donor
type impurities such as for example, phosphorus. Examples of other
dopant impurities include gallium, magnesium, arsenic, calcium,
iron, antimony, nitrogen, silicon, vanadium and beryllium. In a
further embodiment, the dopant impurities are magnetic dopants.
Non-limiting example of magnetic dopants include iron, manganese
and chromium. In another embodiment, the dopant impurities are
optical dopants. Non-limiting examples of optical dopants include
zinc and rare earth elements.
[0022] In one embodiment, the substrate or device layer is a
silicon carbide layer. In another embodiment, the substrate or
device layer is gallium nitride. Non-limiting examples of other
substrate layer or device layer materials include silicon, aluminum
nitride, indium nitride, and aluminum-gallium nitride.
[0023] In one embodiment, the step of providing a carbonized dopant
layer includes disposing a carbon-based dopant material over a
device layer and carbonizing the carbon-based material to form a
carbonized dopant layer. In one embodiment, the carbon-based dopant
material includes a photoresist material and one or more dopant
materials (dopant impurities or source of dopant impurities). In
one embodiment, the carbonized dopant layer includes a carbon
material such as diamond or diamond like carbon.
[0024] The step of disposing a carbon-based dopant material over a
device layer may include the step of coating or depositing the
carbon-based dopant material. Non-limiting examples of methods for
coating a device layer with a carbon-based dopant material include
spin coating.
[0025] In one embodiment, the carbonization process involves
heating at a temperature well above room temperature. For example,
the carbon-based dopant material may be heated at a temperature in
a range from about 500.degree. C. to about 1500.degree. C. to
carbonize the material to form a carbonized dopant layer, wherein
the dopant impurities are embedded in a matrix of carbon. In one
example, the carbon-based dopant material is heated to a requisite
temperature so as to drive out solvents to carbonize it to form a
carbonized dopant layer.
[0026] In one embodiment of the present invention, a carbonized
dopant layer may be deposited over a device layer by vapor
depositing or co-sputtering. The carbonized dopant layer includes
carbon and one or more dopant impurities. In one embodiment, the
carbonized dopant layer includes a carbon material such as diamond
or diamond like carbon.
[0027] The carbonized dopant layer is then heat treated to
thermally diffuse the dopant impurities into the device layer 14.
In a non-limiting example, the heat treatment step is an annealing
step. In one embodiment, the annealing may be carried out at a
temperature selected in a range from about 1000.degree. C. to about
2500.degree. C. In a further embodiment, the annealing may be
carried out at a temperature selected in a range from about
1500.degree. C. to about 2200.degree. C. In one example, the time
duration for the annealing process is about 10 minutes. The
temperature and time duration of the heat treatment may be suitably
selected to provide a desired level of thermal diffusion of dopants
into the device layer.
[0028] In an alternate embodiment, the carbonized dopant layer is
provided over the device layer by forming the carbonized dopant
layer over a different substrate, removing the carbonized dopant
layer from the substrate, and then disposing the carbonized dopant
layer.
[0029] Regardless of the manner in which the carbonized dopant
layer is applied, after the heat treatment the carbonized dopant
layer is typically removed in step 16. In a non-limiting example,
the carbonized layer is burnt or turned into ash in an oxygen
environment and removed.
[0030] FIG. 2 is a flow chart illustrating a method 18 for doping
impurities into a device layer in accordance with a more specific
embodiment of the present invention. The flow chart illustrates the
method for selectively doping dopant impurities into a device
layer. After the step of providing a carbonized dopant layer 20,
the carbonized dopant layer is patterned. In one example, a PECVD
nitride (plasma enhanced chemical vapor deposition of silicon
nitride) layer is deposited over the carbonized dopant layer. A
photoresist layer is then deposited over the nitride layer and is
patterned using photolithography techniques. This is followed by
reactive ion etching of the nitride layer, followed by reactive ion
etching of the carbonized dopant layer. In one example, a
carbonized dopant layer is patterned after carbonization by using
reactive ion etching of oxygen with a suitable mask such as
Si.sub.3N.sub.4. In one embodiment, the nitride layer is deposited
over the carbonized dopant layer to protect the carbonized dopant
layer during the patterning and etching processes. The carbonized
layer is then heat treated to thermally diffuse the dopant
impurities into the device layer 22. The carbonized dopant layer is
then removed in step 24.
[0031] FIG. 3 is a schematic representation of a process for doping
impurities into a device layer in accordance with one embodiment of
the present invention, which is a more specific variation of the
embodiment of FIG. 2. The method 28 includes providing a device
layer or substrate 30. In step 32, a coating 34 of the carbon-based
dopant material is disposed over the device layer 30. In step 36,
the carbon-based dopant material is carbonized to form the
carbonized dopant layer 38. In step 40, the carbonized dopant
material is patterned. In step 43, a protective layer of the
photoresist material 44 is disposed over the patterned layer 42
before step 46, where the carbonized layer is heat treated to
diffuse impurities in the device layer to form impurity doped
regions 48. In step 50, the carbonized dopant layer and the
protective layer are removed.
[0032] An alternate embodiment to the method shown in FIG. 2 is a
method 52 illustrated in the flow chart shown in FIG. 4 for doping
impurities into a device layer in accordance with one embodiment of
the present invention. In the embodiment of FIG. 4, the step of
patterning occurs prior to the step of carbonization of the
carbon-based dopant material. Following disposing a carbon-based
dopant material coating over a device layer 54, the coating is
hardened and patterned in step 56 using for example, conventional
photolithography techniques. In a non-limiting example, the dopant
material disposed over a substrate or device layer may be subjected
to a soft bake, for example at temperature from about 90.degree. C.
to about 110.degree. C. and then subjected to exposure through a
photomask and development of the photoresist. This may be followed
by a hard bake at about a temperature about 300.degree. C. and an
etch to finally pattern the carbon-based dopant material coating.
This is followed by heating the dopant material to a higher
temperature, for example at about 750.degree. C., leading to
carbonization of the dopant material. The carbonized layer is then
heat treated to thermally diffuse the dopant impurities into the
device layer 58. The carbonized dopant layer is then removed in
step 60.
[0033] FIG. 5 is a schematic representation of a process for doping
impurities in accordance with another embodiment of the present
invention. The method 62 includes providing a device layer or
substrate 64 and in step 66 disposing a coating 68 of the
carbon-based dopant material over the device layer 64. In this
embodiment, before the step of carbonizing, the coating 68 is
patterned in step 70 to form a patterned coating 72 of the
carbon-based dopant material. In step 74, a protective layer of a
photoresist material 76 is disposed over the patterned coating 72
of the carbon-based dopant material. The patterned coating 72 of
the carbon-based dopant material and the photoresist material 76
are carbonized in step 78. The carbonized dopant layer is heat
treated in step 82 to diffuse impurities into the device layer to
form impurity doped regions 84. In step 86, the carbonized dopant
layer and the protective layer are removed.
[0034] FIG. 6 is a schematic representation of a process for
fabricating a device, for example a transistor, in accordance with
one embodiment of the present invention. The method 88 includes
providing a device layer or substrate 90. In step 92, a coating of
a first carbon-based dopant material 94 including a first type of
impurities is disposed over the device layer 88. In step 96, the
first carbon-based dopant material is carbonized to form a
carbonized dopant layer 98. In step 100, the first carbonized
dopant material is patterned to form a patterned first carbonized
dopant layer 102. In step 104 a second carbon-based dopant material
including a second type of impurities is deposited over the
patterned first carbonized dopant layer and is carbonized to form a
second carbonized dopant layer 106. Part of the second carbonized
dopant layer 106 is directly in contact with the device layer 90.
In step 108, the two dopant layers 102 and 106 are annealed to
cause thermal diffusion of a first type of impurities and a second
type of impurities into the device layer 90 to form a first dopant
type regions 110 and a second dopant type region 112 sandwiched
between the first dopant type regions 110 and forming junctions
with the first dopant type regions 110 on either side of region
112. In step 114, the two dopant layers 102 and 106 are
removed.
[0035] In one embodiment, the first dopant type comprises at least
one acceptor type dopant (p type) and the second dopant type
comprises at least one donor type dopant (n type), such that a
p-n-p transistor device structure is formed. In another embodiment,
the first dopant type comprises at least one donor type dopant (n
type) and the second dopant type comprises at least one acceptor
type dopant (p type), such that an n-p-n transistor device
structure is formed.
[0036] Many semiconductor devices include regions doped differently
from adjacent layers or regions. In one example, the method
illustrated in FIG. 3 can be used to form a MOSFET device. For
example, a MOSFET has source and drain regions in contact with and
differently doped from a base layer. If the device layer 30 in FIG.
3 is a P-type base layer, then heavily n-doped source and drain
regions 48 can be formed as illustrated in FIG. 3. A gate
dielectric layer can be deposited on top of the P-type base layer
and a gate electrode and source and drain contacts can be deposited
to complete the device. The method can be suitably altered to form
many different semiconductor device structures and all such method
embodiments fall within the scope of this invention. Non-limiting
examples of such devices structures include diodes, transistors,
FETs, MOSFETs, JFETs, etc.
[0037] FIG. 7 is a schematic representation of a process for
forming a device structure, including formation of a graded dopant
region in a device layer in accordance with one embodiment of the
present invention. The method 114 includes providing a device layer
or substrate 116. In step 118 a coating of a first carbon-based
dopant material 120 including one or more impurities is disposed
over the device layer 116. In step 122, the first carbon-based
dopant material is carbonized to form a carbonized dopant layer
124. In step 126 the carbonized dopant layer is heat treated to
diffuse impurities in the device layer to form a doped region 128.
In step 130, the carbonized dopant layer is removed. In step 132, a
second carbon-based dopant material is deposited over the doped
region 128 and is carbonized to form a second carbonized dopant
layer 134. In one embodiment, a second carbon-based dopant layer
includes the same impurities as the first carbon-based dopant
layer. In another embodiment, the second carbon-based dopant layer
includes impurities different from the first carbon-based dopant
layer. In step 136, the second carbonized dopant layer is heat
treated to thermally diffuse the impurities of the second
carbon-based dopant layer into the previously doped region 128. In
addition, the impurities of the first carbon-based dopant layer are
driven further in and a gradation in the concentration of the
impurities in the device layer results, leading to a graded dopant
region 137, having differently doped regions or regions with
different dopant concentration 138 and 139. In step 140, the second
carbonized dopant layer is removed. As used herein, a graded dopant
region or layer refers to a region or layer having a distribution
of dopants that is not uniform. For example, the region 137 could
have a gradual or continuous change in the dopant concentration
from the carbonized dopant layer end to the device layer end. In
another example, the graded region 137 could have two or more zones
of different dopant concentrations but substantially uniform
concentration within the zone. As shown in FIG. 7, the graded
dopant region has two zones, 138 and 139, of different dopant
concentrations.
[0038] In another embodiment, impurities are diffused into a device
layer or substrate by heat treating a carbonized dopant layer to
form a doped region or layer with a first thickness and a first
dopant concentration. Subsequent to the removal of the carbonized
dopant layer after heat treatment, an undoped carbonized dopant
layer is disposed over the device layer and subjected to heat
treatment. This leads to a formation of a modified dopant region or
layer with a thickness greater than the first thickness and a
dopant concentration lower than the first concentration.
[0039] In another embodiment of the present invention as shown in
FIG. 8, more than one type of dopant impurities may be mixed with a
photoresist to form a carbon-based dopant material. In the method
142 shown in FIG. 8, both p type and n-type dopants (for example,
boron and phosphorous) may be mixed with the resist and the coating
148 applied to the device layer 144 as illustrated in step 146. The
layer is carbonized in step 50. Upon heat treatment 154, the p-type
and n-type dopants in the carbonized layer 152 will diffuse at
different rates and to different depths of the device layer 144
forming a first region 156 with substantially a first type of
dopants and a second region 158 with substantially a second type of
dopants. In one embodiment, such differential diffusion will give
rise to a p-n junction formation. If the device layer into which
the dopants are diffused into is an n-type layer initially for
example, and if the p-type dopants diffuse deeper into the device
layer than the n-type dopants, upon diffusion of the dopants an
n-p-n device structure such as a transistor is formed.
[0040] Without further elaboration, it is believed that one skilled
in the art can, using the description herein, utilize the present
invention to its fullest extent. The following examples are
included to provide additional guidance to those skilled in the art
in practicing the claimed invention. The examples provided are
merely representative of the work that contributes to the teaching
of the present application. Accordingly, these examples are not
intended to limit the invention, as defined in the appended claims,
in any manner.
EXAMPLE 1
[0041] In one example a carbon-based dopant material is prepared by
mixing a polymer photoresist (Shipley's AZ1518 or AZ1512) and a
significant source of dopant (boron), tri-methyl-borate. The
mixture is then evenly coated on a silicon carbide wafer by
applying the mixture and spinning the silicon carbide wafer. The
silicon carbide wafer coated with a carbon-based dopant layer is
then annealed in a non-oxidizing ambient to drive off hydrogen and
oxygen, leaving a carbonized dopant layer heavily laden with the
boron impurity. The doped layer is patterned using
photolithography, or is selectively etched away to accomplish
selective area doping. To protect the exposed silicon carbide
surface during the high temperature annealing step, the exposed
area is then coated with an undoped photoresist. The silicon
carbide wafer coated with the doped and patterned carbonized dopant
layer is then annealed at a temperature of about, 1800.degree. C.
to about 2100.degree. C., during which the impurities diffuse into
the SiC wafer. This diffusion of impurities is expected to
electrically alter the silicon carbide material in only the areas
adjacent to the carbonized dopant layer. On short wave UV light
illumination, areas with boron impurity are expected to fluoresce
yellow for 6H--SiC or green-yellow for 4H--SiC.
EXAMPLE 2
[0042] In another example, a carbon-based dopant material is
prepared by mixing a polymer photoresist (Shipley's AZ1518 or
AZ1512) and a significant source of dopant (magnesium),
Mg(OH).sub.2. The mixture is then evenly coated on a gallium
nitride wafer by applying the mixture and spinning the gallium
nitride wafer. The gallium nitride wafer with the carbonized dopant
layer is then annealed at temperature of about 1000.degree. C. to
about 1500.degree. C., during which the impurities diffuse into the
gallium nitride wafer.
[0043] Embodiments of the present invention are expected to provide
selective doping and high quality surface with little damage to the
lattice.
[0044] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
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